In conventional crane-monitoring arrangements it is a common practice to provide a device for monitoring the loading of the boom of a crane having a key-actuated switch or the like which automatically operates upon an overloading of the boom, i.e. the application of a loading moment to the boom in excess of the maximum permissible loading, thereby immobilizing the crane-boom drive. Thereafter the system can be released by operating the key-actuated switch.
Such systems, of course, create difficulties in practice because interruption of the operation of the crane to the point that personnel having control over the key-operated switch must be present to render the crane usable again creates a severe difficulty.
Furthermore, when the crane exceeds the maximum permissible load only for short periods which are not of significant concern, the automatic operation of the immobilizing device is highly objectionable.
Finally, it is important, especially with rented cranes and the like, to appreciate the degree to which the crane has been used at previous operations so as to enable maintenance and supervision practices to correspond to the usage of the crane.
Conventional systems for this purpose have proved to be unsatisfactory.